JAGANNATH GUPTA INSTITUTE OF ENGINEERING AND TECHNOLOGY
A
PRESENTATION
ON
“INTERMEDIATE BAND QUANTUM DOT SOLAR CELL”
CONTENTS Photovoltaic Conventional solar cell
Introduction Working Limitations
Energy bands in solids Intermediate band solar cell Quantum dot Intermediate band quantum dot solar
cell Introduction Construction Working Advantages Applications Limitations
Introduction to Photovoltaic
Generations of voltage
from photons
Light energy ( photons)
are converted into
electrical energy
( voltage).
This conversion is called
“ photovoltaic effect”.
Photovoltaic Generations
First generation: silicon
wafer-based solar cells
Second generation: thin-
film deposits of semiconductors
Third generation: photo-
electrochemical cells
Fourth generation:
composite photovoltaic
technology
Solar Cell
The solar cell (or photovoltaic cell) is a device that converts light energy into electrical energy.
Fundamentally, the device needs to fulfill only two functions:
1. Photo-generation of charge carriers (electrons and holes) in a light-absorbing material.
2. Separation of the charge carriers to a conductive contact that will transmit the electricity.
Intermediate band solar cell
The intermediate band (IB) is an electronic band located within the semiconductor band gap, separated from the conduction and the valence band by a null density of states.
Intermediate band solar cells (IBSCs) are photovoltaic devices.
Used to exploit the energy of below band gap energy photons.
Intermediate band Requirements
Higher photocurrent Higher efficiency arising from
absorption of 2 sub-band gap photons to create one electron-hole pair.
High voltage V=(EF,CB- EF,VB)/q
V~Eg for main semiconductor
Essentials for operation 3 quasi-Fermi levels
IB “disconnected” from emitters Need IB half-filled with electrons Non-overlapping absorption coefficients
How can we introduce these intermediate
energy levels in the band gap?
Answer “Introduce Quantum
Dots”
Quantum dots
A quantum dot is a nano meter sized particle of a low band gap material surrounded by a material with larger band gap.
“Artificial atom” with energy levels depending on the dot size and on the band gap difference.
If many quantum dots are placed closed to each other in a lattice one or more intermediate bands can be formed and a new semiconductor with tailored properties has been made.
Quantum Dot
A quantum dot is a portion of matter (e.g., semiconductor) whose excitons are confined in all three spatial dimensions.
Quantum dots have properties combined between
Those of bulk semiconductors
Those of atoms
Salient characteristics of QDs for IBSC
Dot sized shape,
composition
Dot spacing
Dot regularity
Materials
Doping
APPLICATIONS
Photovoltaic devices: solar cells
Biology : biosensors, imaging
Light emitting diodes: LEDs
Quantum computation
Flat-panel displays
Memory elements
Photodetectors
Lasers
What limits performance of these QD IBSC?
Weak absorption of sub-band gap
photons
Low open-circuit voltage
Low currents
Cost
Conclusions
QD SL cells show photo responses extended to longer wavelengths than GaAs control cells, demonstrating current generation from the absorption of sub-bandgap photons.
IBSC theoretically offers a way to significantly increase cell efficiency compared to that of a single-junction solar cell.
Conclusions
Much more work needs to be done before IBSC can
make a major contribution to the PV market.
“ Miles To Go Before I sleep”